Apparatus and method for controlling motors



Jan. 15, 1963 A. T. BACHELER ETAL 3,073,996

APPARATUS AND METHOD FOR CONTROLLING MOTORS Filed Dec. 30, 1958 4 Sheets-Sheet 1 Jan. 15, 1963 A. T. BACHELER ETAL 3,073,996

APPARATUS AND METHOD FOR CONTROLLING MOTORS Filed Dec. 30, 1958 4 Sheets-Sheet 2 Fig. 45

/Free Reel Speed Fig. 2

mo LOAD LINE Armature Voltage aAs|c CURRENT Armature Currgri;

Jan. 15, 1963 A. 1'. BACHELER ETAL 3,073,996

APPARATUS AND METHOD FOR CONTROLLING MOTORS Filed Dec. 50, 1958 4 Sheets-Sheet 3 POWER SUPPLY UNIT AV DRlVE wnuesses F; 3A INVENTORS 20 7 Albert T. Bucheler, William G. Helmroth 3 and John M. Cochran B 2 $3 0: 7 ATTORNEY I 1963 A. 'r. BACHELER ETAL 9 APPARATUS AND METHOD FOR CONTROLLING MOTORS Filed Dec. 30, 1958 4 Sheets-Sheet 4 23ov.- 460V Y AV DRIVE Resistance in Ohms 4 Capacity in Microfarads f A Inductance in Henries United States Patent Ofifice 3,073,996 APPARATUS AND METHOD FUR CONTROLLING MOTORS Albert T. Bacheler, Eggertsville, William G. Helmrath,

Depew, and John M. Cochran, Williamsville, N.Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 30, 1958, Ser. No. 783,952 6 Claims. (Cl. 318-6) This invention relates to the art of motor control and has particular relationship to the control of the torque and speed of a motor subjected to varying loads. In its specific aspect, the subject matter of this invention is typified by a control for a drive for a reel on which is wound a web that has been passed through a processing line. For example, a film strip which is passed through a coating line may be wound on the reel.

A motor driving such a reel is subjected to loads which vary over a wide range and the variation of which may be relatively abrupt. During normal operation, when the web is being wound on the reel, the diameter of the reel gradually increases. It is then desirable that the torque of the motor be increased to correspond to the increasing radius at the point where the web is being wound on the reel. In addition, it is desirable that at any speed of the motor the torque remain relatively constant. Abrupt changes in the torque at any speed would tend to jerk and possibly rupture the web. In processing and winding operations of the type under consideration, it may also occur that the web is broken at a point between the motor and the region where the web leaves the processing line or in the line itself. Under such circumstances, the motor, if uncontrolled, might freewheel at a very high speed and cause severe damage. In addition, between the completion of any winding operation and the start of a succeeding winding operation, it is desirable that the motor driving the reel remain energized. It is desirable that in both of the latter eventualities the speed of the motor shall not become excessively high.

The Word freewheel as applied to the reel motor or winding motor means the operation of this motor supplied with power but with the reel or winder not connected by the web to the processing line.

It is then broadly an object of this invention to provide apparatus and a method for controlling the speed and torque of the motor which, while having general applicability, shall be particularly suitable for so controlling a motor driving a reel for winding a web which has passed through a processing line that the motor shall have the proper speed torque characteristics under its different conditions of operation.

Another broad object of this invention is to provide apparatus and a method for controlling a motor in such manner that when the motor is loaded its torque increases gradually as the loading increase and its speed drops correspondingly, and when the motor is unloaded, its speed is sharply limited.

Another object of this invention is to provide novel speed and torque control apparatus for a motor.

A further object of this invention is to provide a novel P 3,073,996 Patented Jan. 15, 1953 achieve the desired torque variation under loaded condi' tions and to limit sharply the speed of the motor under unloaded conditions. Specifically, the signal for changing the current reference potential is derived by comparing the potential across the motor with a motor-potential reference potential. When the latter reference potential is higher than the potential across the motor corresponding to a loaded condition of the motor, a given proportion of the difference between the reference potential and the motor potential is added to the motor-current reference potential. This, in turn, demands that the current drawn by the motor increase correspondingly, and this increase is effected by controlling the power supply unit for the motor. When the motor is unloaded and is freewheeling, the potential across the motor becomes greater than the motor-potential reference, and under these circumstances, a substantially higher proportion of the difference between the motor potential and the motor-potential reference potential is subtracted from the motor-current reference potential so that the power supply unit is actuated to supply substantially less power to the motor and the speed of the motor is limited. Thus, under loaded conditions, the torque of the motor and its speed follows a predetermined desired pattern, and under unloaded conditions, the speed of the motor is limited.

The novel features considered characteristic of this invention are disclosed generally above. The invention itself both as to its organization and as to its method of operation, together with additional objects and advantages thereof, will be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a combined circuit and block diagram showing a preferred embodiment of this invention;

FIG. 2 is a graph illustrating the operation of FIG. 1;

FIGS. 3A and 3B together constitute a circuit diagram of a modification of this invention; and

FIGS. 4A and 4B together constitute a circuit diagram similar to FIGS. 3A and 3B but showing magnitudes of the various components included in apparatus in accordance With this invention which has been constructed and found to operate highly satisfactorily.

FIGS. 4A and 4B are presented here, not with the intention of in any way limiting the invention disclosed herein but for the purpose of aiding those skilled in the art in practicing this invention.

The apparatus shown in FIG. 1 includes a Motor, a Power Supply Unit and a Control Unit. The Motor is of the shunt type having a rotor 11, a shunt field winding 13 which may be excited by a constant direct-current potential. The rotor 11 is connected to drive a reel R which winds a web W. The processing line through which the web W passes is driven by an adjustable voltage direct-current drive which includes a motor-generator set and which will be referred to in this application and in the drawing as AV Drive. For control purposes, a potential is derived across terminals 15 and 17 from the generator (not shown) of this AV Drive. This potential serves to indicate the speed at which the web W is passing out of the processing line towards the reel R. The Power Supply Unit may be of any type available in the art. Specifically, it may be an electronic unit having discharge devices (not shown) through which the motor current is supplied. The discharge devices (not shown) are usually provided with control circuits controlling the current transmitted by the devices and thus controlling the current conducted by the Motor. The Power Supply Unit may be energized by supply conductors L1 and L2 which are adapted to be connected to the buses of a commercial single-phase supply through the usual disconnects or circuit breakers (not shown).

The Control Unit includes a current transformer CT coupled to the conductor L1 and capable of producing a potential corresponding to the current conducted by L1 and thus to the current supplied to the rotor 11. The secondary of the current transformer CT is shunted by a resistor R3 which, in turn, is connected through a rectifier RX3 across a second resistor R4. A direct current potential having a polarity as indicated is produced across the latter resistor R4. This potential corresponds to the current drawn by the rotor 11. This potential is compared to a current-reference potential derivable from a variable resistor P4 which is connected across a power supply of any suitable type. The polarity of the currentreference potential P4 is opposed to the polarity of the potential derivable from the current transformer CT. The current-reference potential P4 may be set to determine the current to be drawn by the motor in the absence of loading conditions requiring that this current be modified.

The apparatus shown in FIG. 1 also includes a variable resistor P3 connected across the rotor 11. The potential produced across this resistor P3 corresponds to the speed of the Motor. The polarity of this potential for opera tion of the Motor in a direction such as to cause the reel R to wind, is as indicated in FIG. 1. The resistor P3 is connected to terminals 15 and 17 so that its potential is compared to the potential derivable from the processing line. The connection includes a pair of resistors R1 and R2 across which rectifiers RXl and RX2 and variable resistors P2 and P1 respectively are connected. Rectifier RX is poled so that when the potential between 15 and 17 is greater than the potential derivable from P3, current ilows through RXl and through R2 and P1 in parallel. Rectifier RX2 is poled so that when the potential across P3 exceeds the potential between 15 and 17, the current flows through RX2 and through R1 and P2 in parallel. The adjusting arm 19 of P1 is connected to the Power Supply Unit; the adjusting arm 21 of P2 is connected to P4. The negative terminal of the resistor R4 across which the potential derived from the current transformer is impressed is also connected to the Power Supply Unitfl The potential between the adjusting arm 19 of P1 and the negative terminal 23 of the resistor R4 is thus impressed in the Power Supply Unit so as to control the conduction through the rotor 11. When this potential is of positive polarity, it tends to decrease the supply of power to the rotor 11 and when it is of negative polarity, it tends to increase the supply of power to the rotor.

The variable resistor P1 is set so that when RXIL conducts, a predetermined portion of the potential across R2 is added to the potential derived from P4 in the loop which controls the Power Supply Unit. The variable resistor P2 is set so that when RX2 conducts, a substantially higherproportion of the potential across R1 than the proportion derivable from R2 through P1 is subtracted from the potential across P4 in the control loop for the Power Supply Unit. The conduction through RXl and P1 corresponds to the condition under which the potential between 15 and 17 exceeds the potential derived from P3. This is the condition under which the Motor is loaded. In this case, a smaller proportion of the potential determined by the loading is added to the potential from P4- to increase the power supplied to and the torque of the Motor to correspond to the increase in the desired loading. When the potential between 15 and 17 is smaller than the potential derived from P3, the conduction is through RXZ and P2, and a larger proportion of the difference is subtracted from the potential derived from P4. This corresponds to a freewheeling condition of the Motor, and the larger signal effectively limits the speed of the motor.

The operation of the apparatus shown in FIG. 1 may be considered with reference to FIG. 2 which is a graph in which armature voltage, which is proportional to the speed of the Motor, is plotted vertically and armature current, which is proportional to the load or the torque of the motor, is plotted horizontally. The full lines at an angle present the voltage-current or speed-torque characteristic of the Motor. The right-hand branch of this plot which has a high negative slope corresponds to the operation during the loaded condition of the Motor when the web W is being wound on the reel. The left-hand branch of this plot which has a small negative slope corresponds to the freewheeling condition of the Motor. The vertical broken line designated Basic Current represents the characteristic which the Motor would have if the difference between potential 15-17 and the potential tapped from P3 were zero. The current or speed corresponding to the vertical broken line is called the basic current or basic speed.

When the Motor is winding the web W on the reel R and the diameter of the web is increasing, the angular velocity of the Motor is being gradually reduced. Since the rate at which the web is fed towards the reel R and which is measured by the potential 1517 remains unchanged, the latter potential is in this phase of the operation greater than the voltage derived from P3. A smaller proportion of this voltage is added to the referencevoltage P4, and the current drawn by the Motor and its torque is correspondingly increased as represented by the right hand branch of the plot. This increase is adequate to provide for the increased torque demanded by the increase in radius of the point of the reel at which the web is wound.

If the web W is ruptured or the reel R is filled and removed from the spindle, the speed of the Motor would tend to become high. Under such circumstances, the voltage derived from P3 exceeds 1517 and the reference potential derivable from P4 is reduced by a large portion of the difference. In this case, the current supplied to the Motor is correspondingly reduced, and the Motor is pre vented from operating at a very high speed. With the voltage across the Motor exceeding the reference voltage 1517, the Motor operation follows the left-hand branch of the plot in FIG. 2 until the Motor reaches a point of operation at which the power input to the Motor is just sufiicient to overcome the frictional and other losses of the Motor. This point is represented by the intersection of the broken line labelled No Load Line, on the lefthand branch. At this point stabilization is achieved, and

the Motor operates at the corresponding speed and torque.

With the apparatus shown in FIG. 1, the Motor is thus controlled so that it has characteristics corresponding to tors L3, L4 and L5, which are adapted to be connected braking resistor 21R through contact 36 of contactor F. The rotor 31 drives a reel R which winds a web W.

The Power Supply Unit includes a Scott-connected transformer 1T, the primary lTP of which is energized from the conductors L3, L4 and L5. The transformer IT has power supply secondaries 1TS1, 1TS2, 1TS3 and 1TS4 which are star connected and supply potentials in quadrature. The Power Supply Unit includes control transformers ST and 9T energized from secondaries 1TS2 and 1TS3 respectively. The secondaries 8TS and 9T8 we connected together at their intermediate points and provide control potentials which are also in quadrature corresponding to the secondaries 1TS2 and 1TS3.

The Power Supply Unit also includes a plurality of power thyratrons 7T U, STU, 9TU and IOTU. Each of these thyratrons includes an anode 41, a cathode 43 and a control electrode 45. The cathodes 43 of all the thyratrons 7TU through TU are. connected to a common conductor AL5 which, in turn, is adapted to be connected to one brush of the rotor 31 through contacts 47 of a main contactor F. The anodes 41 of thyratrons 7TU through 10TU are connected respectively to the secondaries 1TS1 through 1TS4 through the primaries 3TP1, 3TP2, 3TP3 and 3TP4 of a current transformer 3T from which a signal corresponding to the current drawn by the Motor is derivable. The signal is derivable across a loading resistor 38R across the secondaries 3TS of 3T. The neutral point J2 of the secondaries 1TS1 through 1TS4 is adapted to be connected to the other brush of rotor 31 through a conductor 48, the series field winding 35 and the contacts 51 of contactor F.

One terminal of secondary 8T5 is connected to the control electrode 45 of 7TU through a grid resistor 49; the other terminal is similarly connected to the control electrode 45 of 9TU. The potential across the section of STS connected to 7TU lags the potential across 1TS1 in phase by 90. Thus, a potential is impressed on the control electrode of 7TU which lags the anode potential of 7TU in phase by 90. The same relationship exists between the anode potential of 9TU and the control potential. The secondary 9TS is similarly connected to the control electrodes 45 of STU and 10TU providing a similar phase-displaced control potential. The neutral junction 11 of the secondaries STS and 9T8 is connected through a conductor ALI to the Control Unit and through this Control Unit to the conductor ALS. The Control Unit has the effect of superimposing a direct current potential on the alternating current potential supplied by the secondaries STS and 9T S. This potential sets the phase at which the thyratrons 7TU through 101" U are fired to correspond to the operation of the Control Unit.

The Control Unit includes a discharge device lTU having an anode 61, a cathode 63 and a control electrode 65. The device may be a high-vacuum pentode, the screen and suppressor grids 67 and 69 of which are properly connected to provide etfective operation of the device. The discharge device 1TU is supplied with direct current potential from a rectifier including device 4TU, reactor 1X, capacitor 1C, andresistors 1R, 2R, 4R. The rectifier is energized from a transformer 2T deriving its power from a winding 1TS5 of the transformer IT. The output of 4TU is suitably filtered by the reactor IX and the capacitor 1C. The capacitor 1C is shunted by the resistorslR, 2R, 4R which form a voltage divider from which the various voltages necessary for lTU are derived. The positive terminal of the rectifier 4TU-1X-1C is connected to the anode 61 of ITU through an anode resistor 3R. The cathode 63 oflTU is connected to the junction of 2R and 4R. Between the anode 61 and the cathode 63, a regulator tube 11TU and a resistor 6R are connected in series. The conductor ALl is connected to the junction J3 of the tube 11TU and resistor 6R. While device 1TU is performing, a control function potential variations between the anode 61 and cathode 63 are im- 6 pressed across 11TU and 6R. Since 11TU absorbs a constant potential, these variations of the potential across 1TU, appear entirely across 6R.

Between the anode 61 and the control grid 65, a capacitor 2C and a resistor 5R are connected. Thi capacitor 2C is shunted by a contact 71 of the contactor F in the stand-by condition of the apparatus and during operation serves to control the acceleration of the Motor. With the contact 71 closed, the control grid 65 is connected directly to the anode 6i, and the discharge device ITU has its maximum conductivity so that the drop across GR is a minimum. With contact 71 open capacitor C controls the rate at which the potential on grid 65 charges and thus the acceleration of the Motor.

The discharge device lTU is controlled by an armaturecurrent responsive network NC, a biasing network NB and an armature-voltage responsive network NA. The current-responsive network NC derives a voltage from the resistor 38R across the secondary 3T5 of the current transformer. The network NC includes a rectifier ZTU through which a capacitor 4C is charged. The capacitor 4C is shunted by a variable resistor IP and a fixed resistor 36R. The variable resistor may be short-circuited by a contact 73 which may be the contact of a relay which is closed when the Motor is to be accelerated abruptly. The variable resistor 1? is set to set the basic torque (see FIG. 2) at which it is desired that the Motor operate. It is about this basic torque that the torque of the Motor is varied responsive to the speed.

The biasing network NB is supplied through a rectifier RX4 from a transformer 4T energized from a secondary 1TS5 of transformer IT. The rectifier is shunted by a fixed resistor 42R and variable resistors SP and 3?. The variable resistor SP is set to set the maximum torque at which the Motor operates, and the variable resistor 31 is set to set the maximum armature voltage which the Motor can have and thus to set the maximum speed at which the Motor operates. The negative terminal of the rectifier RX4 is connected to the control grid 65 of the discharge device 1TU through a grid resistor 7R.

The network NA includes a variable resistor 4F and a fixed resistor 37R for setting the magnitude of the voltagereference potential. The voltage reference potential is derived from the generator of the AV Drive which controls the feed of the web W to the take-up reel R and is represented in FIGS. 3A and 33 by positively and negatively labelled conductors 81 and 83; the positive conductor 81 being grounded. The conductors 31 and 83 are shunted by variable resistor 4? and fixed resistor 37R. The magnitude of the voltage-reference potential is set by 4?.

The potential across the Motor is derivable through a pair of resistors 44R and 45R adapted to be connected in series across the rotor 31 through front contacts 51 and 47 of contactor F. Resistor 44R is shunted by capacitor 3C which tends to suppress transient voltages. The network NA also includes resistors 39R, 40R, 41R and a variable resistor 2P. These resistors are connected in series between the ground conductor 81 and the negative terminal of the network NC. The adjustable arm of the variable resistor 2P is connected directly to the cathode 65 of the discharge device ETU. Resistor 41R is of substantial magnitude compared to 2?, 39R and The network NA also includes rectifiers 3TUA and STUB which may be sections of a double diode, for example, a 6H6 and which operate selectively in dependence upon the relationship between the magnitudes of the reference potential and the potential across the rotor 31. When the voltage-reference potential (8183) exceeds the potential across the rotor ALS is electrically negative relative to the ground conductor 81 and when the potential (81-3) is less than the rotor potential ALS is electrically positive relative to the ground conductor 81. Section STUA is so connected that when conductor ALS is negative relative to ground, positive current flows in a network including 39R, 40R, 2? and 3TUA between ground and ALfi.

In this network, ttlR is shunted by capacitor 50 which performs a smoothing function. Rectifier 3TUB is so connected that when conductor AL is positive relative to ground, current flows in a network extending fgroin ALS through 3TUB, 3P, 5P, 36R, 1P, 41R, 2P 40R and 39R. Smoothing capacitor 6C is connected between the adjust able arm of 2P and AL5 and smoothing capacitor 7C across 3TUB.

The control circuits of thyratrons 7TU through itlTU' are connected so that these thyratrons are controlled in dependence upon the variation of the potential across ITU. The control electrodes 45 of 7TU through ltlTU are connected to junction 13 through conductor ALl and associated sections of secondaries STS and 9T5. The cathodes 43 of 7TU through 101 U are adapted to be connected through contacts 47 armature 31, contacts 51, resistor 35R, resistors 4P, 37R, 39R, 40R, 2? and 4R to the negative terminal of 6R. The phases of the potentials derivable from 8T5 and 9T8 lags the corresponding anode potentials on 7TU through ltlTU by 90. Thus the conduction of 7TU through 10TU is deterininad by the potential across 6R which is in effect the anode-cathode potential across lTU.

It is seen that when AL5 is negative relative to ground the drop between ALS and ground appears across resistors 39R, 40R and variable resistor 2P. The adjustable arm resistor 2? is connected to the cathode 63, and the control circuit of ITU includes the upper part of 2P, 41R, 1P, 36R, 5P, 3P and IR. The potential across the upper part of resistor 2P is then impressed between the control grid 65 and the cathode 63 through the rotor-current responsive potential and the reference potential derivable from 5? and 3P in such a sense as to reduce the conduction 1TU. The positive potential of conductor AL1 would then be increased to increase the conduction of thyratrons 7TU through lttTU. Since only that part of potentiometer 2? from the slider to the anode of 3TUA is in the control grid-cathode circuit of iTU, and 2P is connected between ground and AL5 in series with the resistors 40R and 39R which are not common to the control grid-cathode circuit of ITU, the potential introduced into this control grid-cathode circuit is less than that between ground and AL5.

When conductor ALS is electrically positive relative to ground and 3TUB is conducting, the control circuit of ITU may be regarded as having two parallel paths, one through STUB and the other through 41R. The former circuit extending from the cathode 63 includes the lower part of 2P, MR, 39R, 37R, upper part of 4?,

4411, STUB, lower part of 3P, 7R, 65. The latter circuit extending from the cathode 63 includes upper part: of 2P, 41R, 1P, 36R, lefthand part of 5P, 3?, 7R, grid 65. Since the latter circuit includes 41R, which is of high impedance, the former circuit including STUB gov erns the conduction 1TU. Now in normal operation the grid 65 is biased negatively relative to the cathode, and all the drop in the former circuit is between grid 65 and cathode 63. The cathode is connected to the adjusting arm of 2P which is in effect connected to the ground; the grid is in eflect connected through 3TUB which has a low impedance to the conductor ALS. Thus, the whole potential between AL5 and ground is impressed between the grid 65 and the cathode 63. The polarity of this potential is such as to increase the positive potential of the grid 65 relative to the cathode 63 and thus to de back contact 95. The coil of relay ICR is connected are deenergized.

across secondary lTSti through the back contact 95 of 40R. The coil of contactor F is adapted to be connected across 1TS6 through the front contacts $1 of 10R and the back contacts 950i? 4CR. The coil of tCR is connected across braking resistor 21R.

In the quiescent condition of the apparatus L3, L4, L5 1CR, 4CR and F are then deenergized. The braking resistor 21R is then connected across rotor 31 through contacts 36 of F. Since contacts '71 of F :are closed, 1TU isset for initial maximum conduction and sets thyratron 7TU through 10TU for minimum conduction. Since IT is deenergized device ITU, thyratrons 5 7TU through 10TU and networks NA, NB, NC are deenergized.

Preparatory to an operation resistors 3P and 51 are set to correspond to the desired armature voltage limit and the desired maximum torque, 4? is set to correspond to the desired voltage setting and 2? to the desired torque taper.

The apparatus is set into operation by starting the treating line and energizing conductors L3, L4 and L5. Transformer IT is then energized and potential appears across 1TS5 and 1TS6. Anode potential is supplied to 1TU through 1T S5 but initially 1TU is highly conducting because contacts 71 are closed. Relay lCR is actuated from 1TS6 closing contacts 91 and 93. At contact 93, a circuit is closed which causes the voltage-reference potential to appear between conductors 81 and 83. Thus, contact 91 of contactor F is actuated.

The circuit through armature 31 and thyratrons 7TU through 10TU is then completed and the circuit through the braking resistor 21R is opened. Relay 4CR remains unenergized so that contact 95 remains closed. Rotor 31 and field 35 are now supplied with current but initially the current is low because of the conduction of 1TU. The potential derivable from network NC is then substantially lower than the reference potential derivable from NB. Initially also the potential across rotor 31 is substantially lower than the reference potential derivable from resistor 4P. ALS is then negative relative to ground and the efiective control circuit for lTU includes 65, 7R, 3P, the left-hand part of SP, 36R, the right-hand part of 1?, 41R, the upper part of 2?, and 63. The upper part of 2P delivers a set part of the potential between ALS and ground. Substantial negative potential thus-appears on the control electrode. 65 and the potential between the grid 65 and the cathode 63 drops to a substantial negative magnitude at a rate dependent on the charging of capacitor 20. As the grid potential of lTU becomes more and more negative ALl becomes more positive and the torque and speed of the Motor increases.

Assume that the Motor is connected to reel R and reel R is winding the web W. The speed of the Motor then decreases in dependence upon the increasing radius of the web in the reel and the potential across the rotor decreases so that the negative potential dilferences between ALS and ground increases since the potential from 4P remains unchanged. The grid potential of llTU then increases negatively, ALI becomes more positive and 7TU through 10TU become more and more conducting to increase the torque of the Motor in dependence upon the setting of 2P. If new the web shouldbecome ruptured or the opcratorshould cut the web, the speed of the rotor would then tend to increase above the speed of the motor of the adjustable voltage drive. The rotor potentialwould then increase until the proportion of it appearing across resistor 44R e ualed and then ex- 7R, lower part of SP, 3TUB, 44R, upper part of 4P, 37R, 39R, 40R, lower part of 2P, 63. ln this circuit substantially the whole potential between AL5 and ground is impressed between the grid 65 and the cathode 63 in such a sense as to increase the positive potential of the grid. The conduction of discharge device ITU then increases correspondingly, and the conductivity of thyratrons 7TU through 10TU is correspondingly decreased. Power is then supplied to the Motor at a limited rate, and the speed of the Motor increases only to a small extent to the point at which the power input to the Motor just overcomes the frictional resistances of the Motor and related mechanisms. The Motor then operates at this speed until the apparatus is reset for a winding operation. The speed of the Motor may be limited by setting 3? to the desired setting.

While preferred embodiments of this invention have been disclosed herein, many modifications thereof are feasible. The invention then is not to be restricted except insofar as is necessitated by the spirit of the prior art.

We claim as our invention:

1. In combination, a motor, means connected to said motor for deriving a first potential dependent on the current conducted by the rotor of said motor, means connected to said motor for deriving a second potential dependent on the potential across said rotor, rotor-current reference potential supply means, rotor-potential reference potential supply means, a first variable impedance, a second variable impedance, a first rectifier, a second rectifier, means connecting said variable impedances and said rectifiers in a network in which said rectifiers are connected opposing, said firs-t rectifier is shunted by said first impedance, and said second rectifier is shunted by said second impedance, means connecting in a first series circuit said first potential, said rotor-current reference potential and said network with said firs-t potential and said rotor-current reference potential opposing, and means connecting in a second series circuit said second potential, said rotor-potential reference potential and said network, with said second potential and said rotor-potential reference potential opposing, said reference potentials being connected aiding in the overall circuit formed by said first and second circuits.

2. In combination, a motor, means connected to said motor for deriving a first potential dependent on the current conducted by the rotor of said motor, means connected to said motor for deriving a second potential dependent on the potential across said rotor, rotor-current reference potential supply means, rotor-potential reference potential supply means, a first variable impedance, a second variable impedance, one of said variable impedances being substantially greater than the other, a first rectifier, a second rectifier, means connecting said variable impedances and said rectifiers in a network in which said rectifiers are connected opposing, said first rectifier is shunted by said first impedance, and said second rectifier is shunted by said second impedance, means connecting in a first series circuit said first potential, said rotor-current reference potential and said network with said first potential and said rotor-current reference potential opposing, and means connecting in a second series circuit said second potential, said rotor-potential reference potential and said network, with said second potential and said rotor-potential reference potential opposing, said reference potentials being connected aiding in the overall circuit formed by said first and second circuits.

3. Apparatus for controlling the supply of current from power supply means to a motor driving a reel winding a web comprising first means connected to said motor for deriving a first control potential, herein designated Vlc, dependent on the current conducted by the rotor of said motor, second means connected to said motor for deriving a second control potential, herein designated V3c substantially equal to a predetermined proportion of the potential across said rotor, first reference potential supply means for supplying a first reference potential, herein designated Vlr, second reference potential supply means for supplying a second reference potential, herein designated V21, means connecting said first and second means and said first and second reference-potential supply means in a comparison circuit which produces an error signal, said error signal being dependent on k1 being a constant, when V2r is greater than V3c, and VlcV1r-k2(V3c V2r), k2 being a constant substantially greater than k1, when V30 is greater than V21, and means connecting to said power supply means, said comparison circuit and said motor in a compensating circuit for increasing the power supplied to said motor when said error is negative and for decreasing the power supplied to said motor when said error is positive.

4. In combination, an electric discharge device having an anode, a cathode, and a control electrode, first and second conductors between which a control potential of either polarity is impressed, first rectifier means, second rectifier means, high impedance means, variable impedance means, means connecting one terminal of said variable impedance means to one terminal of said high impedance means, means connecting another terminal of said variable impedance means to said cathode, means connecting another terminal of said high impedance means to said control electrode, means connecting in a first series circuit said first conductor, said second conductor, said first rectifier means, said variable impedance means and said high impedance means, said first rectifier means being poled in said first circuit to conduct with said first conductor electrically positive relative to said second conductor, said one terminal of said variable impedance means being electrically negative relative to said other terminal, of said variable impedance means, and means connecting in a second series circuit exclusive of said high impedance means, said first conductor, said second conductor, said control electrode, said cathode and said second rectifier means, said second rectifier means being poled in said second circuit to conduct when said second conductor is electrically positive relative to said first conductor.

5. In combination, first and second conductors for impressing a control potential, third and fourth conductors for deriving a resulting control potential, first impedance means, second impedance means, said first means being substantially greater than said second means, first rectifier means, second rectifier means, means connecting in a first series circuit said first conductor, said second conductor, said first rectifier means and said second impedance means, with said first rectifier means poled in said first circuit to conduct when said first conductor is electrically positive relative to said second conductor, means connecting in a second series circuit, said first conductor, said second conductor, said second rectifier means and said first impedance means, with said second rectifier means poled in said second circuit to conduct when said second conductor is electrically positive relative to said first conductor, and means connecting said third conductor to said first impedance means and said fourth conductor to said second impedance to derive the potential across both said impedance means.

6. In combination, an electric discharge device having an anode, a cathode, and a control electrode, first and second conductors between which a control potential of either polarity is impressed, first rectifier means, second rectifier means, high impedance means, variable impedance means, means connecting one terminal of said variable impedance means to one terminal of said high impedance means, means connecting another terminal of said variable impedance means to said cathode, means connecting another terminal of said high impedance means to said control electrode, means connecting in a first series circuit said first conductor, said second conductor, said first rectifier means, said variable impedance means and said high 0nd circuit to conduct when said second conductor is electrically positive relative to said first conductor, said second series circuit also including means maintaining said control electrode electrically negative relative to said 5 cathode.

References Cited in the file of this patent UNITED STATES PATENTS Montgomery Mar. 27, 1956 Peoples May 22, 1956 

1. IN COMBINATION, A MOTOR, MEANS CONNECTED TO SAID MOTOR FOR DERIVING A FIRST POTENTIAL DEPENDENT ON THE CURRENT CONDUCTED BY THE ROTOR OF SAID MOTOR, MEANS CONNECTED TO SAID MOTOR FOR DERIVING A SECOND POTENTIAL DEPENDENT ON THE POTENTIAL ACROSS SAID ROTOR, ROTOR-CURRENT REFERENCE POTENTIAL SUPPLY MEANS, A FIRST VARIABLE IMPDEANCE, ENCE POTENTIAL SUPPLY MEANS, A FIRST VARIABLE IMPEDANCE, A SECOND VARIABLE IMPEDANCE, A FIRST RECTIFIER, A SECOND RECTIFIER, MEANS CONNECTING SAID VARIABLE IMPEDANCES AND SAID RECTIFIERS IN A NETWORK IN WHICH SAID RECTIFIERS ARE CONNECTED OPPOSING, SAID FIRST RECTIFIER IS SHUNTED BY SAID FIRST IMPEDANCE, AND SAID SECOND RECTIFIER IS SHUNTED BY SAID SECOND IMPEDANCE, MEANS CONNECTING IN A FIRST SERIES CIRCUIT SAIF FIRST POTENTIAL, SAID ROTOR-CURRENT REFERENCE POTENTIAL AND SAID NETWORK WITH SAID FIRST POTENTIAL AND SAID ROTOR-CURRENT REFERENCE POTENTIAL OPPOSING, AND MEANS CONNECTING IN A SECOND SERIES CIRCUIT SAID SECOND POTENTIAL, SAID ROTOR-POTENTIAL REFERENCE POTENTIAL AND SAID NETWORK, WITH SAID SECOND POTENTIAL AND SAID ROTOR-POTENTIAL REFERENCE POTENTIAL OPPOSING, SAID REFERENCE POTENTIALS BEING CONNECTED AIDING IN THE OVERALL CIRCUIT FORMED BY SAID FIRST AND SECOND CIRCUITS. 